In general, this invention relates to technology for dissolving gas in a liquid. More specifically, it relates to a method and an apparats for dissolving carbon dioxide in waste gas which contains carbon dioxide gas and which is discharged in large quantities from stationary gas generating facilities such as thermal power plants in sea water and isolating it deep in the sea, and to a method of installing the apparatus.
From in the past, carbon dioxide has been representative of water-soluble gases which have been studied for isolation in the sea in order to prevent atmospheric pollution and global warming. Techniques for isolation in the sea of carbon dioxide gas have included (a) a method in which carbon dioxide gas is liquified and then discharged directly deep into the sea, (b) a method in which carbon dioxide gas is formed into dry ice and then dropped directly into the sea, and (c) a method in which carbon dioxide gas is blown directly into shallow seas (having a depth on the order of 200-400 meters) and dissolved.
However, in method (a), large amounts of energy and costs are necessary in order to separate and recover carbon dioxide gas from waste gas and to liquify carbon dioxide gas, and there is much acidification of sea water in the vicinity of where the liquified carbon dioxide is released, so it has the problem of large effects on the environment. In method (b), large amounts of energy and costs are necessary in order to separate and recover carbon dioxide gas from waste gas and to process it into dry ice, and after dropping dry ice directly into the sea, the state of dissolving and dispersion of carbon dioxide is unclear, so it has the problem of poor reliability of isolation in the sea. In method (c), the depth of water where carbon dioxide gas is dissolved and dispersed in the sea is shallow, so there is the problem that the period of time (the period of isolation in the sea) until the carbon dioxide which is dissolved in sea water is again released into the atmosphere is short.
A method and apparatus in which carbon dioxide gas is dissolved in sea water and is isolated by sinking sea water, which has increased in specific gravity due to dissolving carbon dioxide gas, deep into the sea is disclosed in the specification of Japanese Patent No. 2655818.
In such technology, carbon dioxide gas is blown from a pipe forming a short leg of a conduit in the shape of an inverted J having the pipe forming a short leg and a pipe forming a long leg connected at their upper portions to form an inverted J shape, sea water is made to flow in from the lower end of the pipe forming a short leg by the gas lift effect, and carbon dioxide gas is completely dissolved in the sea water by the time the sea water reaches the upper end of the pipe forming a short leg. The pipe forming a long leg of the inverted J-shaped conduit functions as a sinking pipe having its lower end opening onto deep in the sea, and sea water which has increased in density due to the dissolving of carbon dioxide sinks deep into the sea due to gravity.
If a gas is blown into water, the gas becomes bubbles and rises towards the surface of the water. At this time, the surrounding water is pulled by viscosity, The phenomena in which an upwards flow is generated is called the gas lift effect. The above-described method uses the gas lift effect to dissolve water-soluble gas in sea water and isolate it deep in the sea.
However, not all of the water-soluble gas which is supplied into sea water from the lower end portion of the dissolving pipe in the form of the pipe forming a short leg is dissolved in sea water, and a portion thereof remains in the pipe as undissolved gas. Furthermore, there are also cases in which insoluble gas is contained in the gas which is being blown.
In such cases, accumulation of undissolved gas takes place in the inverted J-shaped conduit, and the flow of sea water within the conduit ends up being impeded, so separation and discharge thereof must be carried out, but the separation and discharge are difficult.
If supply is carried out to the sinking pipe in a state in which undissolved gas is contained, the specific gravity of liquid in the sinking pipe decreases, and there is the problem that sinking is not carried out smoothly.
In order to supply only carbon dioxide gas, it is necessary to previously devise a separating means, so cost increases are unavoidable.
In addition, in the conventional technology disclosed in the above-described patent, the apparatus is installed in a region of the sea with a depth from the surface of at least 100 meters, and in sea water with such a depth, maintenance inspection of the apparatus is not easy, and operation must be interrupted if it is raised to above the water surface each time, so it cannot be said to be efficient.
Accordingly, a first object of this invention is to provide a method and apparatus which can easily treat undissolved gas remaining within a pipe and which can dissolve water-soluble gas in sea water and isolate it deep in the sea.
A second object of this invention is to provide a method and apparatus which can dissolve water-soluble gas in sea water and isolate it deep in the sea and which can easily carry out processing of undissolved gas remaining in a pipe even if gas such as ordinary waste gas containing a portion which is not soluble in sea water is injected without modification and which can easily undergo maintenance inspection.
A third object of this invention is to provide an installation method which can easily install such an apparatus in the sea.
The present inventors performed various investigations of means for realizing these objects and obtained the following knowledge.
(1) By placing a vessel having an appropriate space between and connecting a dissolving pipe and a sinking pipe, it is possible to separate within the vessel undissolved gas contained in the gas which is blown, and separation and discharge thereof are easy.
(2) If the above-described vessel is installed on the surface of the sea or in the vicinity thereof, not only installation but also maintenance inspection are easy.
(3) By forming the dissolving pipe, the sinking pipe, and the vessel which connects them as an integrated body, the manufacture and the installation thereof are made still easier.
Here, the present invention is a method of dissolving a water-soluble gas in sea water and isolating it deep in the sea, characterized by connecting a pipe forming a short leg and a pipe forming a long leg to a vessel which is installed in the sea or on the surface of the sea or in the vicinity thereof, with the pipe forming a short leg serving as a dissolving pipe and being maintained in shallow water in the sea, for example, blowing gas containing a water-soluble gas into its open lower end portion, introducing and raising sea water from the lower end of the pipe forming a short leg by the gas lift effect of gas in the pipe forming a short leg and dissolving water-soluble gas contained in the gas in the sea water as the sea water rises within the pipe forming a short leg, diffusing undissolved gas into the atmosphere from the liquid surface within the vessel, using the pipe forming a long leg as a sinking pipe opening onto deep in the sea, and making the sea water within the vessel sink deep into the sea due to the increase in density caused by dissolving of the water-soluble gas and due to the difference in pressure head corresponding to an increase in the liquid surface within the vessel caused by the gas lift effect.
From another standpoint, the present invention is an apparatus for dissolving water-soluble gas in sea water and isolating it deep in the sea, characterized by comprising a vessel installed in the sea or at the surface of the sea or in the vicinity thereof, a pipe forming a short leg which is connected to the vessel and which is open at its lower end portion and which is equipped with, blowing means for gas containing a water-soluble gas and which functions as a dissolving pipe, and a pipe forming a long leg which is also connected to the vessel and which is open at its lower end portion and which functions as a sinking pipe, the vessel functioning to diffuse undissolved gas to the atmosphere from the liquid surface within the vessel.
From yet another standpoint, the present invention is an apparatus for dissolving water-soluble gas in sea water and isolating it deep in the sea, characterized in that it is equipped with an elongated cylindrical structure which is installed at the surface of the sea and houses a small diameter fist vertical pipe and a large diameter second vertical pipe, the cylindrical structure and the second vertical pipe being concentrically constituted, the upper end portions of the first and second vertical pipes are connected through a container section which partitions the interior of the cylindrical structure, the first vertical pipe functions as a dissolving pipe which exhibits a gas lift effect, the second vertical pipe functions as a sinking pipe, and the vessel functions as a separator for undissolved gas, gas containing water-soluble gas is blown from a blowing nozzle mounted near the lower end of the dissolving pipe which opens into the sea and sea water flows into the lower end of the dissolving pipe due to the gas lift effect of the gas in the dissolving pipe, the water-soluble gas contained in the gas is dissolved in sea water as it rises within the dissolving pipe, undissolved gas which did not dissolve in sea water in the dissolving pipe is separated and accumulated in the vessel, the energy possessed by the flow within the dissolving pipe is conserved as potential energy in the rise of the water level and as energy stored in the form of pressure of the undissolved gas, and the sea water in the vessel in which water-soluble gas is dissolved settles to deep in the sea through the sinking pipe, the lower end of which extends further and is open to deep in the sea, due to the increase in density caused by the dissolving of water-soluble gas and the increase in the potential energy of the sea water in the vessel and the energy stored in the form of pressure of the undissolved gas.
In the lower portion of the cylindrical structure, a space for housing a ballast tank for adjusting buoyancy may be provided.
In the vessel, the separated and collected undissolved gas may be discharged to the atmosphere through a discharge pipe and a valve. In addition, it is also possible for the upper portion of the vessel to be open to the atmosphere.
In this manner, according to this invention, the following advantages are obtained.
(1) Regardless of concentration, waste gas containing water-soluble gas such as carbon dioxide can be supplied to sea water.
(2) When the gas lift pressure is inadequate, it is possible to take steps such as increasing the amount of blown gas or decreasing the length of the dissolving pipe in which gas is dissolved.
(3) The length of the dissolving pipe can be adjusted to the optimal length based on dissolving efficiency and the installation environment.
(4) The apparatus can be installed in shallower seas than in the past.
(5) When the proportion of undissolved gas contained in the blown gas is small, the undissolved gas expands as it rises and the proportion of gas bubbles within the dissolving pipe increases and the gas lift effect is decreased, and flow is impeded, but this can be prevented.
(6) By separating undissolved gas and dischanging it through a discharge pipe to the atmosphere, the effects on sea transportation, fishing, and ecosystems in the sea due to disturbance of the water surface by bubbles accompanying the discharge of undissolved gas can be mitigated.
(7) When installing the apparatus in sea water, it is necessary to provide buoyant devices, but by using the above-described vessel as a buoyant device or by integrating the vessel and a buoyant device, it is possible to decrease the overall size of the apparatus as well as to make the installation and mooring of the apparatus in the sea easier.